title: Dissociation of the N-C(alpha) bond and competitive formation of the [z(n) - H](+) and [c(n) + 2H](+) product ions in radical peptide ions containing tyrosine and tryptophan: the influence of proton affinities on product formation.
abstract: Dissociations at the N-C(alpha) bond of tryptophan and tyrosine residues are the prevalent pathways in the fragmentations of radical cations of tripeptides that contain such as residues. This process involves a proton transfer from the beta-carbon of the tryptophan or tyrosine residue to the carbonyl oxygen of the amide group, followed by cleavage of the N-C(alpha) bond, generating low-lying proton-bound dimers that dissociate to give each an ionic and a neutral product. Formation of the [z(n) - H](*+) or [c(n) + 2H](+) ion is a competition between the two incipient fragments for the proton in a dissociating proton-bound dimer.
authors.affiliation: Department of Chemistry and Centre for Research in Mass Spectrometry, York University, Toronto, Ontario, Canada.
authors.forename: Chi-Kit
authors.initials: CK
authors.lastname: Siu
authors.forename: Yuyong
authors.initials: Y
authors.lastname: Ke
authors.forename: Galina
authors.initials: G
authors.lastname: Orlova
authors.forename: Alan C
authors.initials: AC
authors.lastname: Hopkinson
authors.forename: K W
authors.initials: KW
authors.lastname: Michael Siu
mesh_terms: D005609:Free Radicals; D015394:Molecular Structure; D009842:Oligopeptides / Q000737:chemistry*; D010446:Peptide Fragments / Q000737:chemistry; D011522:Protons; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry; D013816:Thermodynamics; D014364:Tryptophan / Q000737:chemistry; D014443:Tyrosine / Q000737:chemistry*
chemical_list: D005609:Free Radicals; D009842:Oligopeptides; D010446:Peptide Fragments; D011522:Protons; D014443:Tyrosine; D014364:Tryptophan